<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outDiv{
            background-color: burlywood;
            width: 500px;
            height: 300px;
            border: 1px solid green;
            margin: 0px auto;
        }

        .innerDiv{
            width: 100px;
            height: 100px;
            border: 1px solid blue;
        }

        .d1{
            background-color: red;
            /* display: inline; */
            float: left;
        }
        .d2{
            background-color: green;
            /* display: inline; */
            float: left;
        }
        .d3{
            background-color: greenyellow;
            /* display: inline; */
            float: left;
        }
    </style>
</head>
<body>
    <div class="outDiv">
        <div class="innerDiv d1">d1</div>
        <div class="innerDiv d2">d2</div>
        <div class="innerDiv d3">d3</div>
    </div>
    
</body>
</html>